Conventionally, for an image sensing apparatus which combines and reads signal charges generated by respective photoelectric conversion elements, a method of driving image sensing elements so as to combine signal charges corresponding to the same color component in vertical transfer registers is considered (refer to Japanese Patent Application Laid-Open No. 2000-253415).
FIGS. 4A and 4B show a conceptual view of combining charges for the same colors in the vertical direction accumulated in image sensing elements covered with a Bayer filter. The Bayer filter has R, G, and B color filters arranged as shown in FIG. 4A. More specifically, lines in which R and G filters are alternately arranged, and lines in which G and B filters are alternately arranged are disposed alternately. When signal charges are combined in the vertical direction, since filters of each color are disposed on every other pixels, a driving unit of the image sensing elements drives the image sensing elements so that signal charges of the pixels arranged in every other lines are combined.
For example, referring to FIG. 4A, pixel signals from a line of R00 and G01 are combined with pixel signals from a line of R20 and G21, then pixel signals of a line of R10 and G11 shown in FIG. 4B are generated. Further, pixel signals from a line of G10 and B11 are combined with pixel signals from a line of G30 and B31, then pixel signals of a line of G20 and B21 are generated. Similarly, pixel signals from a line of R40 and G41 are combined with pixel signals from a line of R60 and G61, then pixel signals of a line of R50 and G51 are generated, and pixel signals from a line of G50 and B51 are combined with pixel signals from a line of G70 and B71, then pixel signals of a line of G60 and B61 are generated. The color order of the combined signals is the same as the Bayer order of the signals before combined.
When signals are combined in the aforesaid manner, the barycenter of each combined signal is located in the center of the two pixels before combined. This makes the barycenters of the combined signals approach each other by two lines as shown in FIG. 4B. Namely, the intervals between the barycenters are unequal in the vertical direction. Therefore, it is necessary to apply camera signal processing conforming to such arrangement to the combined signals. Whereas, when signal charges are separately read from the image sensing elements without being combined for, e.g., sensing a still image, camera signal processing conforming to the normal Bayer arrangement has to be performed. Thus, a camera signal processing unit conforming to a case of reading charge signals without combining them and a camera signal processing unit conforming to a case of combining and reading charge signals for sensing a moving image are needed.